"Karyology of a population of Dugesia benazzii (Tricladida Paludicola) with B-chromosomes". A karyological analysis has been carried out on specimens of the planarian Dugesia benazzii collected in Conca stream (Corsica). In this popu lation, which reproduces mainly by fìssion, only few individuals become sexual; the latter condition, moreover, is not constant. Bothe somaticand germ cells present polysomic. sets with rather large numerica!variations (from 18 to 28 chromosomes). In 85% of the cells examined, B-chromosomes, varying in number from 1 to 4, have also been observed. This study provides also a quantitative analysis of the karyometric data concerning both standard and B-chromosomes.